1. Field of the Invention
The present invention relates to lens barrels having cam barrels with cams and cam followers engaged with the cams for transferring lens holders via the engagement between the cams and the cam followers.
2. Description of the Related Art
In order to change focal lengths of optical systems of zoom lenses in lens barrels, a mechanism including cams and cam followers engaged with the cams for transferring lenses that are integrated with the cam followers is in widespread use. More specifically, for example, a cylindrical cam barrel including three cams having the same locus formed on the inner surface thereof at regular intervals and a lens holding member including cam followers corresponding to the cams and holding a lens in the center thereof are engaged with each other via the cams. The lens holding member is supported by the cam barrel so as not to be rotatable and so as to be movable using the cams in connection with the rotation of the cam barrel.
In this mechanism, backlash between the cams and the cam followers can cause degradation of captured images and blurring of images during zooming due to wobbling of the lens. However, without backlash, the load required for rotating the cam barrel can be increased by the friction between the cams and the cam followers, and abrasion of the cams and the cam followers can be increased due to the friction.
In order to solve these problems, a method for urging a cam follower toward a cam using an elastic force of an elastic member has been discussed. According to this method, backlash can be reliably eliminated, and the force for urging the cam follower toward the cam can be adjusted using the elastic force of the elastic member. With this, the driving load can be reduced, and the abrasion can also be reduced.
In order to urge the cam follower, a method in which the cam follower is guided so as to be reciprocable and an end of the cam follower is pressed toward the cam using a compression spring has been discussed.
However, according to the method in which the end of the cam follower is pressed using the compression spring, the compression spring is disposed so as to extend in a direction of urging the cam follower, and therefore, at least a structure accommodating the compression spring in the urging direction is required. Therefore, the lens holding member cannot be reduced in size in a radial direction thereof.
According to Japanese Registered Utility Model No. 2567258, a plate spring is used as the elastic member for urging the cam follower. A portion of the cam follower is narrowed, and the plate spring is hooked on the narrowed portion. Since the engaging portion between the cam follower and the lens holding member extends in a radial direction of the lens holding member, the lens holding member cannot be reduced in size in a radial direction thereof. Moreover, the length of the engaging portion between the cam follower and the lens holding member needs to be increased in order to prevent the cam follower from falling off the lens holding member. This also prevents the reduction in the size of the lens holding member in a radial direction thereof. Moreover, falling of the cam follower from the lens holding member cannot be completely prevented even when the length of the engaging portion between the cam follower and the lens holding member is increased.